Secondary battery

ABSTRACT

A secondary battery includes: an electrode assembly including a positive electrode plate and a negative electrode plate; an exterior housing that has an opening and houses the electrode assembly; and a sealing plate ( 2 ) that seals the opening. The exterior housing and the sealing plate ( 2 ) form a battery case. A deformable member ( 19 ) that deforms when the pressure inside the battery case reaches a prescribed value or higher and a gas release valve ( 18 ) that breaks when the pressure inside the battery case reaches a prescribed value or higher to release gas inside the battery case to the outside of the battery case are provided in the sealing plate ( 2 ). A metallic reinforcing member ( 30 ) is connected to the inner surface of the sealing plate ( 2 ).

This application is a continuation of U.S. application Ser. No.16/312,395, filed on Dec. 21, 2018, which is a National Stage ofInternational Application No. PCT/JP2017/023469, filed on Jun. 27, 2017,which claims priority to Japanese priority application No. 2016-128239filed on Jun. 29, 2016, which are hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates to a secondary battery.

BACKGROUND ART

Hybrid electric vehicles and electric vehicles that use secondarybatteries such as non-aqueous electrolyte secondary batteries have comeinto widespread use. In hybrid electric vehicles and electric vehicles,a plurality of secondary batteries are connected in series or paralleland used as an assembled battery.

It is necessary for these secondary batteries to have high reliability,and a safety mechanism is provided for the secondary batteries. Forexample, a gas release valve is provided in a battery case. The gasrelease valve breaks when the pressure inside the battery case reaches aprescribed value or higher to release the gas inside the battery case tothe outside of the battery case.

One technique proposed to improve the reliability of a secondary batterywhen it is overcharged is to provide a short circuit mechanism that isactivated when the pressure inside the battery case reaches a prescribedvalue or higher and causes positive and negative electrodes to beelectrically short-circuited outside an electrode assembly (PTL 1below).

CITATION LIST Patent Literature

PTL 1: Japanese Published Unexamined Patent Application No. 2011-018645

SUMMARY OF INVENTION Technical Problem

One object of the present invention is to provide a more reliablesecondary battery.

Solution to Problem

A secondary battery according to one aspect of the present inventionincludes:

an electrode assembly including a positive electrode plate and anegative electrode plate;

an exterior housing that has an opening and houses the electrodeassembly; and

a sealing plate that seals the opening,

wherein the exterior housing and the sealing plate form a battery case,

wherein a deformable member that deforms when the pressure inside thebattery case reaches a prescribed value or higher and a gas releasevalve that breaks when the pressure inside the battery case reaches aprescribed value or higher to release gas inside the battery case to theoutside of the battery case are provided in the sealing plate,

wherein a metallic reinforcing member is connected to the inner surfaceof the sealing plate, and

wherein the reinforcing member is positioned so as to face the gasrelease valve.

To improve the reliability of a secondary battery, it is contemplated toprovide a gas release valve for a sealing plate included in a batterycase and to provide, for the sealing plate, a deformable member such asan invertible plate forming, for example, a short circuit mechanism thatis activated when the pressure inside the battery case reaches aprescribed value or higher. In this case, the gas release valve and thedeformable member are each formed to have a smaller thickness than themain body of the sealing plate. Therefore, when the gas release valveand the deformable member are disposed in the sealing plate, thestrength of the sealing plate is lower than that when only the gasrelease valve is disposed in the sealing plate and the deformable memberis not disposed in the sealing plate. When the pressure inside thebattery case increases, the sealing plate may deform. In this case, thepressure at which the deformable member is activated and the pressure atwhich the gas release valve is activated may deviate from their intendedvalues.

In the secondary battery having the structure described above, the gasrelease valve and the deformable member disposed in the sealing platecan cause a reduction in the strength of the sealing plate. However,since the metallic reinforcing member is connected to the inner surfaceof the sealing plate, the deformation such as bending of the sealingplate caused by an increase in the pressure inside the battery case canbe reduced. Therefore, the activation pressure of the deformable memberand the activation pressure of the gas release valve can be stabilized.This allows the secondary battery to be more reliable.

Advantageous Effects of Invention

The present invention can provide a highly reliable secondary battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(a) is a top view schematically showing the structure of asecondary battery in one embodiment of the present invention, and FIG.1(b) is a cross-sectional view of the secondary battery.

FIG. 2 is a partial enlarged cross-sectional view around a positiveelectrode terminal of the secondary battery shown in FIG. 1(b).

FIG. 3 is a partial enlarged cross-sectional view around a negativeelectrode terminal of the secondary battery shown in FIG. 1(b).

FIG. 4 is an illustration showing the inner surface side of a sealingplate with components attached thereto.

FIG. 5 is a perspective view showing a reinforcing member in theembodiment.

FIG. 6 is a cross-sectional view around a joint between the reinforcingmember and the sealing plate, the cross-sectional view being taken inthe lengthwise direction of the sealing plate.

FIG. 7 is an enlarged perspective view around a connection portion ofthe reinforcing member in a modification.

FIG. 8 is an enlarged view around a joint between the reinforcing memberand the sealing plate in the modification.

FIG. 9 is an enlarged view around a joint between the reinforcing memberand the sealing plate in another modification.

FIG. 10 is a perspective view of the reinforcing member in amodification.

FIG. 11 shows a development of the reinforcing member in a modification.

FIG. 12 shows a development of the reinforcing member in anothermodification.

FIG. 13 is a cross-sectional view around a joint between the reinforcingmember and the sealing plate, the cross-sectional view being taken inthe lengthwise direction of the sealing plate.

FIG. 14 is a perspective view of a rectangular secondary battery in amodification.

FIG. 15 is a cross-sectional view of the rectangular secondary batteryin the modification.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be described in detail withreference to the drawings. However, the present invention is not limitedto the following embodiments.

As shown in FIGS. 1(a) and 1(b), in a rectangular secondary battery 50in an embodiment, an electrode assembly 3 serving as a power generationelement and an electrolytic solution are housed in a battery case 40.The electrode assembly 3 has a structure in which a positive electrodeplate (not shown) and a negative electrode plate (not shown) are woundor stacked with a separator (not shown) therebetween. The electrodeassembly 3 shown in FIG. 1(b) is a wound electrode assembly includingthe long positive electrode plate and the long negative electrode platethat are wound with the separator therebetween. A wound positiveelectrode core-exposed portion 4 is formed at one end of the electrodeassembly 3, and a wound negative electrode core-exposed portion 5 isformed at the other end.

The battery case 40 includes: an exterior housing 1 that has an openingand houses the electrode assembly 3; and a sealing plate 2 that sealsthe opening of the exterior housing 1. The exterior housing 1 has aclosed-end rectangular cylindrical shape with an upper opening.Preferably, the exterior housing 1 and the sealing plate 2 are made of ametal. Preferably, they are each made of aluminum, an aluminum alloy,stainless steel, iron, an iron alloy, etc. An insulating sheet 20 isdisposed between the exterior housing 1 and the electrode assembly 3.

The positive electrode plate used may be prepared by forming a positiveelectrode active material layer containing a positive electrode activematerial on a surface of a metallic positive electrode core. Thenegative electrode plate used may be prepared by forming a negativeelectrode active material layer containing a negative electrode activematerial on a surface of a metallic negative electrode core. Thepositive electrode plate and the negative electrode plate have thepositive electrode core-exposed portion 4 with no active electrode layerat its end and the negative electrode core-exposed portion 5 with noactive electrode layer at its end, respectively. The positive electrodeplate and the negative electrode plate are disposed such that thepositive electrode core-exposed portion 4 and the negative electrodecore-exposed portion 5 extend in opposite directions. The positiveelectrode core-exposed portion 4 is connected to a positive electrodeterminal 7 through a positive electrode current collector 6. Thenegative electrode core-exposed portion 5 is connected to a negativeelectrode terminal 10 through a negative electrode current collector 9.The positive electrode terminal 7 and the negative electrode terminal 10pass through their respective through holes formed in the sealing plate2 and are fixed to the sealing plate 2. On the outer surface side of thesealing plate 2, the positive electrode terminal 7 is connected to apositive electrode external conductive member 8, and the negativeelectrode terminal 10 is connected to a negative electrode externalconductive member 11.

A liquid injection hole 16 for injecting the electrolytic solution isformed in the sealing plate 2. The liquid injection hole 16 is sealedwith a sealing member 17 after injection of the electrolytic solution. Agas release valve 18 is disposed in the sealing plate 2. The gas releasevalve 18 breaks when the pressure inside the battery case 40 reaches aprescribed value or higher to thereby release the gas inside the batterycase 40 to the outside of the battery case 40.

A deformable member 19 is disposed in the sealing plate 2. Thedeformable member 19 deforms when the pressure inside the battery case40 reaches a prescribed value or higher and comes into contact with thenegative electrode external conductive member 11 directly or throughanother conductive member. Preferably, the pressure at which the gasrelease valve 18 breaks is set to be higher than the pressure at whichthe deformable member 19 deforms. The thickness of the gas release valve18 and the thickness of the deformable member 19 are smaller than thethickness of the sealing plate 2. The gas release valve 18 is formed asa thin-walled portion by subjecting the sealing plate 2 to pressworking. The deformable member 19 is connected by welding to the outersurface side of the sealing plate 2 so as to cover a through hole 2 xformed in the sealing plate 2. A gas release valve separate from thesealing plate 2 may be connected by welding to the sealing plate 2 so asto cover the through hole formed in the sealing plate 2. Preferably, agroove is formed in the gas release valve.

When the rectangular secondary battery 50 is a non-aqueous electrolytesecondary battery, it is preferable that the positive electrode core,the positive electrode current collector 6, the positive electrodeterminal 7, and the positive electrode external conductive member 8 areeach made of aluminum or an aluminum alloy. It is preferable that thenegative electrode core, the negative electrode current collector 9, andthe negative electrode terminal 10 are each made of copper or a copperalloy. One part of the negative electrode terminal 10 may be made ofcopper or a copper alloy, and the other part may be made of aluminum oran aluminum alloy. The part made of copper or a copper alloy may bedisposed inside the battery case 40. In this case, it is preferable thatthe negative electrode external conductive member 11 is made of aluminumor an aluminum alloy. The negative electrode terminal 10 may be made ofcopper or a copper alloy. In the negative electrode external conductivemember 11, a portion connected to the negative electrode terminal 10 maybe made of copper or a copper alloy. In this case, it is preferablethat, in the negative electrode external conductive member 11, a portionto which a bus bar is connected is made of aluminum or an aluminumalloy. It is also preferable that bus bars connecting terminals ofadjacent secondary batteries are made of aluminum or an aluminum alloy.

As shown in FIG. 2, the positive electrode terminal 7 passes through athrough hole formed in the sealing plate 2 and is fixed to the sealingplate 2. A gap between the positive electrode terminal 7 and the sealingplate 2 is hermetically sealed with a gasket 21 disposed on the innersurface of the through hole. The positive electrode terminal 7 isconnected to the positive electrode current collector 6 on the innersurface side of the sealing plate 2. The positive electrode terminal 7is connected to the positive electrode external conductive member 8 onthe outer surface side of the sealing plate 2. A first insulating member12 is disposed between the sealing plate 2 and the positive electrodecurrent collector 6. A second insulating member 13 is disposed betweenthe sealing plate 2 and the positive electrode external conductivemember 8. The second insulating member 13 has a through hole 13 a, and afirst protrusion 2 a of the sealing plate 2 is disposed in the throughhole 13 a. The sealing plate 2 and the positive electrode externalconductive member 8 are electrically connected to each other through thefirst protrusion 2 a. The second insulating member 13 may not be used,and the positive electrode external conductive member 8 may be disposeddirectly on the sealing plate 2. Instead of the second insulating member13, a conductive member may be disposed between the sealing plate 2 andthe positive electrode external conductive member 8. The gasket 21 andone of the first insulating member 12 and the second insulating member13 may be formed as a single component. Preferably, the gasket 21, thefirst insulating member 12, and the second insulating member 13 are eachmade of a resin.

The positive electrode terminal 7 is connected by, for example, weldingto the positive electrode current collector 6 on the inner surface sideof the sealing plate 2 and is connected by crimping to the positiveelectrode external conductive member 8 on the outer surface side of thesealing plate 2. Preferably, the crimped portion of the positiveelectrode terminal 7 is connected by welding to the positive electrodeexternal conductive member 8. The positive electrode terminal 7 may beconnected by crimping to the positive electrode current collector 6 onthe inner surface side of the sealing plate 2. The positive electrodeexternal conductive member 8 may not be used, and a flange portion maybe provided in the positive electrode terminal 7. This flange portion isdisposed on the outer surface side of the sealing plate 2.

When an assembled battery is produced by connecting a plurality of therectangular secondary batteries 50 through bus bars, each bus bar may beconnected to the positive electrode external conductive member 8 of asecondary battery 50 at a position spaced apart from the portionconnected to the positive electrode terminal 7 toward the center of thesealing plate 2. Preferably, the positive electrode external conductivemember 8 and the bus bar are each made of aluminum or an aluminum alloy.An opening or a notch may be formed in the positive electrode externalconductive member 8 to form a fuse portion 8 a. In this case, it ispreferable that the fuse portion is formed in the positive electrodeexternal conductive member 8 at a position between the portion connectedto the positive electrode terminal 7 and the portion connected to thebus bar. A fuse portion may be provided in the positive electrodecurrent collector 6. The fuse portions are not essential components.

As shown in FIG. 3, the negative electrode terminal 10 passes through athrough hole formed in the sealing plate 2 and is fixed to the sealingplate 2. A gap between the negative electrode terminal 10 and thesealing plate 2 is hermetically sealed with a gasket 22. The negativeelectrode terminal 10 is connected to the negative electrode currentcollector 9 on the inner surface side of the sealing plate 2. Thenegative electrode terminal 10 is connected to the negative electrodeexternal conductive member 11 on the outer surface side of the sealingplate 2. A third insulating member 14 is disposed between the sealingplate 2 and the negative electrode current collector 9. A fourthinsulating member 15 is disposed between the sealing plate 2 and thenegative electrode external conductive member 11.

The negative electrode terminal 10 is connected by, for example, weldingto the negative electrode current collector 9 on the inner surface sideof the sealing plate 2 and is connected by crimping to the negativeelectrode external conductive member 11 on the outer surface side of thesealing plate 2. Preferably, the crimped portion of the negativeelectrode terminal 10 is connected by welding to the negative electrodeexternal conductive member 11. The negative electrode terminal 10 may beconnected by crimping to the negative electrode current collector 9 onthe inner surface side of the sealing plate 2. The negative electrodeexternal conductive member 11 may not be used, and a flange portion maybe provided in the negative electrode terminal 10. This flange portionis disposed on the outer surface side of the sealing plate 2. The gasket22 and one of the third insulating member 14 and the fourth insulatingmember 15 may be formed as a single component. Preferably, the gasket22, the third insulating member 14, and the fourth insulating member 15are each made of a resin.

As shown in FIG. 3, the through hole 2 x is formed in the sealing plate2, and the deformable member 19 is disposed so as to cover the throughhole 2 x. The peripheral edge of the deformable member 19 is connectedby welding to the sealing plate 2. Preferably, the deformable member 19has a dome portion with its central part protruding toward the innerside of the battery (toward the electrode assembly 3). Preferably, whenthe pressure inside the battery case 40 reaches a prescribed value orhigher, the dome portion deforms so as to protrude toward the outer sideof the battery (toward the negative electrode external conductive member11).

When the rectangular secondary battery 50 is, for example, overcharged,gas may be generated in the battery case 40. In this case, when thepressure inside the battery case 40 exceeds a prescribed value, thedeformable member 19 deforms so as to protrude toward the negativeelectrode external conductive member 11. Then the deformable member 19comes into contact with the negative electrode external conductivemember 11. Since the sealing plate 2 is electrically connected to thepositive electrode external conductive member 8 as described above, thedeformable member 19 is electrically connected to the positive electrodeplate. Therefore, when the deformable member 19 deforms and comes intocontact with the negative electrode external conductive member 11, thepositive electrode plate and the negative electrode plate areelectrically short-circuited outside the electrode assembly 3. Thedeformable member 19 and the negative electrode external conductivemember 11 form a short circuit mechanism 25.

This can prevent further charging current from flowing into theelectrode assembly 3, and energy in the electrode assembly 3 can beconsumed. More preferably, a fuse portion is provided in the positiveelectrode current collector 6 or the positive electrode externalconductor member 8 such that the short circuit current causes the fuseportion to melt to thereby break the conductive path.

By forming the sealing plate 2 by press working, the deformable member19 can be formed integrally with the sealing plate 2. When thedeformable member 19 attached to the sealing plate 2 is formedseparately from the sealing plate 2, it is preferable that thedeformable member 19 is connected by welding to the outer surface sideof the sealing plate 2. The deformable member 19 is preferably made ofthe same metal as the sealing plate 2 and more preferably made ofaluminum or an aluminum alloy. The shape of the deformable member 19 isnot limited to a specific shape, so long as the deformable member 19deforms when the pressure inside the battery case 40 reaches aprescribed value or higher and is electrically connected to the negativeelectrode external conductive member 11.

FIG. 4 is an illustration showing the inner surface side of the sealingplate 2 (the inner side of the battery) with components attachedthereto. In FIG. 4, the position of the gas release valve 18 isindicated by a broken line. As shown in FIG. 4, a metallic reinforcingmember 30 is connected to the inner surface of the sealing plate 2.Preferably, the reinforcing member 30 is positioned so as to face thegas release valve 18. The reinforcing member 30 can be produced bybending a plate-shaped metal member.

FIG. 5 is a perspective view of the reinforcing member 30. The upperside in FIG. 5 is the electrode assembly 3 side of the rectangularsecondary battery 50, and the lower side is the sealing plate 2 side.The reinforcing member 30 includes a main body 30 a disposed so as toface the gas release valve 18, leg portions 30 b extending from the mainbody 30 a toward the sealing plate 2, and connection portions 30 cdisposed at forward ends of the leg portions 30 b. The connectionportions 30 c are connected by welding to the sealing plate 2. Four legportions 30 b are disposed at edges of the main body 30 a. Openings areformed between adjacent leg portions 30 b. A pair of first openings 30 dare disposed so as to be opposed to each other in the lengthwisedirection of the sealing plate 2, and a pair of second openings 30 e aredisposed so as to be opposed to each other in the widthwise direction ofthe sealing plate 2. The gas is discharged through the first openings 30d and the second openings 30 e.

To further improve the reliability of the rectangular secondary battery50, the gas release valve 18 is provided in the sealing plate 2, and thedeformable member 19 included in the short circuit mechanism 25 isfurther provided. In this case, the strength of the sealing plate 2 maydecrease. If the strength of the sealing plate 2 decreases, the sealingplate 2 may bend and deform as the pressure inside the battery case 40increases. Alternatively, the expansion of the electrode assembly 3 maycause the exterior housing 1 to deform, and this deformation may causethe sealing plate 2 to deform. The deformation of the sealing plate 2may cause a problem in that the operating pressure of the deformablemember 19 or the gas release valve 18 is not stabilized.

However, in the rectangular secondary battery 50, the metallicreinforcing member 30 is attached to the inner surface side of thesealing plate 2. In this case, even when the gas release valve 18 isprovided in the sealing plate 2 and the deformable member 19 is furtherprovided, the deformation of the sealing plate 2 can be reduced.Therefore, the operating pressure of the gas release valve 18 and theoperating pressure of the deformable member 19 are stabilized, and thesecondary battery can be more reliable.

Preferably, a fifth insulating member 35 is disposed between thereinforcing member 30 and the electrode assembly 3. In the rectangularsecondary battery 50, an insulating tape serving as the fifth insulatingmember 35 is applied to the electrode assembly 3 at a position facingthe reinforcing member 30. Preferably, the electrode assembly 3 includesa plurality of wound electrode assemblies, and an insulating tape thatbinds the plurality of wound electrode assemblies together is used asthe fifth insulating member 35.

Preferably, the connection portions 30 c of the reinforcing member 30are connected to the sealing plate 2 at positions around the gas releasevalve 18. Preferably, the gas release valve 18 is disposed so as to besurrounded by the connection portions 30 c. In this case, the operatingpressure of the gas release valve 18 can be stabilized more reliably.

Preferably, the connection portions 30 c of the reinforcing member 30are connected to the sealing plate 2 at positions between the deformablemember 19 and the gas release valve 18 and between the gas release valve18 and the liquid injection hole 16 in the lengthwise direction of thesealing plate 2. In this case, the deformation of the sealing plate 2can be reduced more effectively.

A preferred structure will be described below.

FIG. 6 is a cross-sectional view around a joint between the sealingplate 2 and the sealing plate 2 of the reinforcing member 30, thecross-sectional view being taken in the lengthwise direction of thesealing plate 2. Preferably, a second protrusion 2 b is formed on thesealing plate 2 such that an end of a connection portion 30 c of thereinforcing member 30 is in contact with the second protrusion 2 b asshown in FIG. 6, and the end of the connection portion 30 c and thesecond protrusion 2 b are connected to each other by, for example, laserwelding. In this case, preferably, a plurality of second protrusions 2 bare formed on the sealing plate 2, and the second protrusions 2 b areconnected by welding to the respective connection portions 30 c.Preferably, the second protrusions 2 b are disposed at ends of therespective connection portions 30 c that are on the side opposite to theleg portions 30 b. With this structure, the deformation of the sealingplate 2 can be reduced more effectively.

Recesses may be formed in the sealing plate 2, and the connectionportions 30 c of the reinforcing member 30 may be fitted into therecesses. In this case, preferably, the connection portions 30 c of thereinforcing member 30 are welded to edges of the recesses to therebyconnect the reinforcing member 30 to the sealing plate 2. With thisstructure, the strength of the sealing plate 2 can be more effectivelyimproved.

FIG. 7 is an enlarged perspective view around a connection portion 30 cof the reinforcing member 30 in a modification. As shown in FIG. 7, athin-walled portion 30 x is formed in part of a connection portion 30 c,and this thin portion 30 x can be connected by welding to the sealingplate 2. In this case, the reinforcing member 30 can be connected bywelding to the sealing plate 2 using relatively small energy, so that aload during welding is prevented from being applied to the gas releasevalve 18.

FIG. 8 is an enlarged plan view around the joint between the sealingplate 2 and a connection portion 30 c of the reinforcing member 30 inthe modification. As shown in FIG. 8, a third protrusion 2 c is formedon the sealing plate 2, and a notch 30 y is formed in the connectionportion 30 c. The third protrusion 2 c is fitted to the notch 30 y. Thenthe third protrusion 2 c is connected by, for example, laser welding tothe edge of the notch 30 y. With this structure, the deformation of thesealing plate 2 can be reduced more effectively. The third protrusion 2c is not limited to the circular cylindrical protrusion and may be aprism-shaped protrusion or a protrusion having another shape.

FIG. 9 is an enlarged plan view around the joint between the sealingplate 2 and a connection portion 30 c of the reinforcing member 30 inanother modification. As shown in FIG. 9, a third protrusion 2 c isformed on the sealing plate 2, and a connection opening 30 z is formedin the connection portions 30 c. The third protrusion 2 c is fitted tothe connection opening 30 z. Then the third protrusion 2 c can beconnected by, for example, laser welding to the edge of the connectionopening 30 z. With this structure, the deformation of the sealing plate2 can be reduced more effectively.

FIG. 10 is a perspective view of the reinforcing member 30 in amodification. In the reinforcing member 30 shown in FIG. 5, the legportions 30 b are disposed at opposite edges, with respect to thelengthwise direction of the sealing plate 2, of the main body 30 a.However, in the reinforcing member 30 in this modification, the legportions 30 b are disposed at opposite edges, with respect to thewidthwise direction of the sealing plate 2, of the main body 30 a. Inthis structure, when the gas release valve 18 breaks, the gas in theexterior housing 1 can be discharged to the outside of the battery moresmoothly. When the reinforcing member 30 shown in FIG. 10 is used, apair of third openings 30 f are disposed so as to be opposed to eachother in the lengthwise direction of the sealing plate 2, and a pair offourth openings 30 g are disposed so as to be opposed to each other inthe widthwise direction of the sealing plate 2.

FIGS. 11 and 12 are developments of reinforcing members 30 inmodifications. Positions indicated by broken lines are boundariesbetween the main body 30 a and the leg portions 30 b and boundariesbetween the leg portions 30 b and the connection portions 30 c. In theabove embodiment, the reinforcing member 30 used is made of aluminum oran aluminum alloy. However, each of the reinforcing members 30 in thesemodifications includes portions made of different metals.

As shown in FIG. 11, in the reinforcing member 30 in one of thesemodifications, a second metallic portion 32 made of a second metalhaving a higher Young's modulus than aluminum and an aluminum alloy isstacked on a first metallic portion 31 made of aluminum or an aluminumalloy used as a first metal. In this case, the deformation of thesealing plate 2 can be reduced more effectively. The second metallicportion 32 is disposed on the main body 30 a composed of the firstmetallic portion 31. More preferably, the melting point of the secondmetal is higher than the melting point of the first metal. In this case,even when the temperature of the rectangular secondary battery 50increases, the deformation of the sealing plate 2 can be prevented moreeffectively.

The first metal is preferably aluminum or an aluminum alloy. The secondmetal is preferably copper, a copper alloy, iron, an iron alloy, nickel,a nickel alloy, etc. No particular limitation is imposed on the methodfor connecting the first metallic portion 31 to the second metallicportion 32. The second metallic portion 32 may be connected by weldingto the reinforcing member 30 made of the first metal. They may beconnected to each other by, for example, crimping. For example, they maybe connected to each other by forming a protrusion on the first metallicportion 31 made of the first metal, inserting the protrusion into anopening or a notch in the second metallic portion 32, and then expandingthe diameter of the forward end of the protrusion. Alternatively, a cladmaterial including the first metal and the second metal may be used. Inthis case, the clad material is subjected to bending to form thereinforcing member 30.

The reinforcing member 30 may be made of copper, a copper alloy, iron,an iron alloy, nickel, a nickel alloy, etc. When the second metal iscopper or a copper alloy, it is preferable that the second metallicportion 32 is not exposed at the outer surface of the reinforcing member30. For example, it is preferable that, in the reinforcing member 30used, a member made of copper or a copper alloy is contained inside thereinforcing member 30 made of aluminum or an aluminum alloy.

It is preferable that the second metallic portion 32 is disposed notonly on the main body 30 a but also on the leg portions 30 b, as shownin FIG. 12. It is also preferable that the second metallic portion 32 isdisposed also on the connection portions 30 c, as shown in FIG. 12.However, as shown in FIG. 12, it is preferable that, in at least part ofthe connection portions 30 c, the first metallic portion 31 made of thesame metal as the sealing plate 2 is exposed.

FIG. 13 is a cross-sectional view around a joint between the reinforcingmember 30 and the sealing plate 2, the cross-sectional view being takenin the lengthwise direction of the sealing plate 2. In FIG. 13, theupper side is the side toward the electrode assembly 3, and the lowerside is the side toward the sealing plate 2. When the sealing plate 2and the reinforcing member 30 are viewed in a direction parallel to theinner surface of the sealing plate 2 and extending in the widthwisedirection of the sealing plate 2, it is preferable that α>β holds, asshown in FIG. 13. Here, α(°) is the angle between a leg portion 30 b ofthe reinforcing member 30 and the inner surface of the sealing plate 2,and β(°) is the angle between the inner surface of the sealing plate 2and a straight line L that connects P1 to P1. Here, P1 is an end of thejoint between the reinforcing member 30 and the sealing plate 2, whichend is located on the side toward the main body 30 a. P2 is an end ofthe boundary between the main body 30 a of the reinforcing member 30 andthe leg portion 30 b, which end is located on the side toward thesealing plate 2. In this case, the deformation of the sealing plate 2can be reduced more effectively.

FIG. 14 is a perspective view of a rectangular secondary battery 150 ina modification. FIG. 15 is a cross-sectional view of the rectangularsecondary battery 150. Differences between the rectangular secondarybattery 150 in this modification and the rectangular secondary battery50 described above will be described below. Portions that will not bedescribed have substantially the same structures as those in therectangular secondary battery 50.

As shown in FIGS. 14 and 15, a battery case 140 includes: an exteriorhousing 101 that has an opening and houses an electrode assembly 103;and a sealing plate 102 that seals the opening of the exterior housing101. The exterior housing 101 has a bottom 101 a, a pair of first sidewalls 101 b, and a pair of second side walls 101 c. The area of eachsecond side wall 101 c is smaller than the area of each first side wall101 b. The opening of the exterior housing 101 is disposed at a positionopposed to the bottom 101 a. The area of the opening of the exteriorhousing 101 sealed with the sealing plate 102 is smaller than the areaof each second side wall 101 c.

In this structure, the sealing plate 102 can have the same area as thesmallest one of the six main outer surfaces of the battery case 140.This is more preferable because, even when the pressure inside thebattery case 140 increases, the sealing plate does not easily deform.

As shown in FIG. 15, a positive electrode core-exposed portion 104 and anegative electrode core-exposed portion 105 are disposed at an edge ofthe electrode assembly 103 on the side toward the sealing plate 102. Thepositive electrode core-exposed portion 104 is electrically connected toa positive electrode terminal 7 and a positive electrode externalconductive member 8 through a positive electrode current collector 106.The negative electrode core-exposed portion 105 is electricallyconnected to a negative electrode terminal 10 and a negative electrodeexternal conductive member 11 through a negative electrode currentcollector 109. The positive electrode core-exposed portion 104 includinga stack of a plurality of layers protrudes from the electrode assembly103, and the negative electrode core-exposed portion 105 including astack of a plurality of layers protrudes from the electrode assembly103.

In this case, it is preferable that the electrode assembly 103 is awound electrode assembly and is housed in the exterior housing 101 suchthat the winding axis of the wound electrode assembly is perpendicularto the sealing plate 102. In the wound electrode assembly 103, thecentral portion of the electrode assembly 103 tends to expand afterrepeated charging and discharging cycles. When the central portion ofthe electrode assembly 103 expands, the exterior housing 101 is pressedoutward by the electrode assembly 103 and is thereby deformed. Thedeformation of the exterior housing 101 may cause the sealing plate 102to deform.

In the above structure, the sealing plate 102 can be easily disposed ata position spaced apart from the central portion of the electrodeassembly 103, so that the deformation of the sealing plate 102 caused bythe deformation of the exterior housing 101 can be reduced effectively.Preferably, the electrode assembly 103 disposed in the battery case 140includes a plurality of wound electrode assemblies. The use of theplurality of wound electrode assemblies is more advantageous in reducingthe deformation of the battery case 140 than the use of one large woundelectrode assembly.

In the rectangular secondary battery 150, the sealing plate 102 has thesame area as the smallest one of the six main outer surfaces of thebattery case 140. In this case, it is preferable that the reinforcingmember 30 has the shape shown in FIG. 10. This allows the length of thereinforcing member 30 in the lengthwise direction of the sealing plate102 to be reduced. Therefore, the reinforcing member 30 is preventedfrom interfering with other components.

In the rectangular secondary battery 150, the sealing plate 102 has thesame area as the smallest one of the six main outer surfaces of thebattery case 140. In this case, when the reinforcing member 30 has theshape shown in FIG. 5, it is preferable that the liquid injection hole16 is located between two connection portions 30 c. This can reduce thedeformation of the sealing plate 102 more effectively.

<Others>

In the above embodiment, the short circuit mechanism has the structurein which the deformable member 19 is electrically connected to thepositive electrode plate, but this is not a limitation. It is onlynecessary that the deformable member 19 be formed in the sealing plate2. For example, the sealing plate 2 and the deformable member 19 may notbe electrically connected to the positive electrode plate and thenegative electrode plate during normal use of the secondary battery.However, in this structure, the sealing plate 2 and the deformablemember 19 are electrically connected to one of the electrode plates whenthe deformable member 19 is activated. For example, two deformablemembers may be disposed in the sealing plate 2. The positive electrodeexternal conductive member is disposed above one of the deformablemembers, and the negative electrode external conductive member isdisposed above the other deformable member. In this case, when one ofthe deformable members deforms and is electrically connected to thepositive electrode external conductive member and the other deformablemember deforms and is electrically connected to the negative electrodeexternal conductive member, the positive electrode plate and thenegative electrode plate are electrically short-circuited.

No particular limitation is imposed on the type of the rectangularsecondary battery 50 in the present invention. No particular limitationis imposed on the structure of the electrode assembly 3. The electrodeassembly 3 may be a wound electrode assembly prepared by winging a longpositive electrode plate and a long negative electrode plate through aseparator. The electrode assembly 3 may be a stacked electrode assemblyprepared by stacking a plurality of positive electrode plates and aplurality of negative electrode plates through separators.

The present invention is particularly effective when applied to anon-aqueous electrolyte secondary battery. Known materials can be usedfor the positive electrode, the negative electrode, the separator, theelectrolytic solution, etc. It is particularly preferable that amaterial that generates a gas when the rectangular secondary battery 50is overcharged is added to the positive electrode plate or theelectrolytic solution. For example, lithium carbonate may be added tothe positive electrode active material layer. Cyclohexylbenzene, forexample, may be added to the electrolytic solution.

In the examples shown in the above embodiment, the gas release valve 18is disposed integrally with the sealing plate 2. However, a gas releasevalve 18 prepared separately from the sealing plate 2 may be connectedby welding to the sealing plate 2 so as to cover a through hole formedin the sealing plate 2. When both the deformable member 19 and the gasrelease valve 18 are connected by welding to the sealing plate 2, it ispreferable that the deformable member 19 is welded to the outer surfaceside of the sealing plate 2 and the gas release valve 18 is welded tothe inner surface side of the sealing plate 2.

REFERENCE SIGNS LIST

-   -   50 rectangular secondary battery    -   40 battery case    -   1 exterior housing    -   2 sealing plate    -   2 a first protrusion    -   2 b second protrusion    -   2 c third protrusion    -   2 x through hole    -   3 electrode assembly    -   4 positive electrode core-exposed portion    -   5 negative electrode core-exposed portion    -   6 positive electrode current collector    -   7 positive electrode terminal    -   8 positive electrode external conductive member    -   8 a fuse portion    -   9 negative electrode current collector    -   10 negative electrode terminal    -   11 negative electrode external conductive member    -   12 first insulating member    -   13 second insulating member    -   14 third insulating member    -   15 fourth insulating member    -   16 liquid injection hole    -   17 sealing member    -   18 gas release valve    -   19 deformable member    -   20 insulating sheet    -   21 gasket    -   22 gasket    -   25 short circuit mechanism    -   30 reinforcing member    -   30 a main body    -   30 b leg portion    -   30 c connection portion    -   30 d first opening    -   30 e second opening    -   30 x thin-walled portion    -   30 y notch    -   30 z connection opening    -   30 f third opening    -   30 g fourth opening    -   31 first metallic portion    -   32 second metallic portion    -   35 fifth insulating member    -   101 exterior housing    -   101 a bottom    -   101 b first side wall    -   101 c second side wall    -   102 sealing plate    -   103 electrode assembly    -   104 positive electrode core-exposed portion    -   105 negative electrode core-exposed portion    -   106 positive electrode current collector    -   109 negative electrode current collector    -   140 battery case    -   150 rectangular secondary battery

1. A secondary battery comprising: an electrode body including apositive electrode plate and a negative electrode plate; a battery casecontaining the electrode body; a terminal attached to the battery case;a conductive member having an opening adjacent to the electrode body; adeformation plate that seals the opening, and a current collector;wherein the positive electrode plate or the negative electrode plate iselectrically connected to the terminal via the current collector, thedeformation plate, and the conductive member, the current collector hasa through-hole, the deformation plate includes a thick portion which hasa larger thickness than a surrounding area, in a central part of, thethick portion is disposed to face the through-hole, the currentcollector is welded to the thick portion to form a weld, and thedeformation plate deforms when an internal pressure of the battery casereaches a predetermined value or higher, and the deformation of thedeformation plate causes electrical disconnection between the positiveelectrode plate or the negative electrode plate and the terminal.
 2. Thesecondary battery according to claim 1, wherein the weld penetrates thecurrent collector and is connected to the deformation plate, and theweld does not penetrate the deformation plate.
 3. The secondary batteryaccording to claim 1, wherein a portion of the current collector distantfrom the through-hole is welded to the thick portion to form the weld.4. The secondary battery according to claim 3, wherein the deformationplate has a protrusion, which protrudes toward the electrode body, in acentral part, and the thick portion includes the protrusion.
 5. Thesecondary battery according to claim 1, wherein as the weld is viewed ina direction perpendicular to the deformation plate, the weld has asubstantially annular shape, and the weld having a substantially annularshape is located so as to surround the through-hole.
 6. The secondarybattery according to claim 5, wherein the weld having a substantiallyannular shape includes two substantially annular welds that are adjacentin a radial direction of the deformation plate.
 7. The secondary batteryaccording to claim 1, wherein, as the weld is viewed in a directionperpendicular to the deformation plate, the weld has a zig-zag pattern.8. The secondary battery according to claim 1, wherein the deformationplate has an annular first groove on its surface adjacent to theelectrode body and an annular second groove on its surface adjacent tothe terminal, in a radial direction of the deformation plate, at leastpart of the first groove is located outward of the second groove, and inthe radial direction of the deformation plate, a width of the secondgroove is larger than a width of the first groove.
 9. The secondarybattery according to claim 8, wherein a depth of the first groove islarger than a depth of the second groove.
 10. The secondary batteryaccording to claim 8, wherein the first groove includes a bottom, afirst side wall, and a second side wall, the first side wall is locatednearer to a center of the deformation plate than the second side wall,and an angle of the second side wall to the bottom is larger than anangle of the first side wall to the bottom.
 11. The secondary batteryaccording to claim 1, wherein the deformation plate has a taperedportion at its periphery that is an edge adjacent to the terminal. 12.The secondary battery according to claim 1, wherein the terminal and theconductive member are integrally formed as one component.